The present invention refers to an improved apparatus for handling on a large-scale basis, and in an orderly sequential manner, containers made of thermoplastic material, in particular polyethylene terephtalate (PET) and polypropylene (PP), by submitting appropriate semi-finished moulded parts generally known as xe2x80x9cparisonsxe2x80x9d or xe2x80x9cpreformsxe2x80x9d to a so-called blow-moulding process.
In particular, the present invention can be used in a most advantageous manner when the described apparatus is associated to a preform production plant, i.e., a plant that is also known as a single-stage one, but can, of course, be effectively used also in connection with plants that are fed with previously produced preforms to only carry out the final blow-moulding phase (two-stage plants).
As a matter of fact, these processes for the production of the above cited kinds of containers are generally known to be able to be schematically divided into two basic topologies, single-stage and two-stage processes.
In two-stage processes, a previously moulded preform or parison in a substantially amorphous state is heated up again to its preferred molecular orientation temperature, at which it is then blow-moulded to the desired shape. As used in this particular context, the term xe2x80x9ctwo-stage processxe2x80x9d, or simply xe2x80x9ctwo-stagexe2x80x9d, is intended to mean any process that produces a preform or parison which must subsequently be heated up again from room temperature to the respective blow-moulding temperature.
On the contrary, single-stage processes are so defined owing to the fact that they are capable of moulding the so-called preform or parison, and transferring the same preform or parison from the injection or extrusion mould (after it has cooled down to some appropriate temperature) to a conditioning station where the preform or parison is allowed to evenly balance down to a preferred molecular orientation temperature. The preform or parison is then transferred to a blow-moulding mould, where it is moulded to the desired shape.
The state of the art concerning the techniques implemented for solving the various problems in connection with the processes of injection-moulding or extrusion and blow-moulding of the preforms, as well as the synchronization of all these processes with each other in view of increasing the productivity of the whole production plant, is exhaustively described in the European patent application EP 0 768 165, filed by the same Applicant, which also describes the most significant patent literature existing on the matter and to which reference should therefore be made.
Both above cited types of production methods involve the use of a (per sxc3xa8 known) blow-moulding station and the therewith associated handling means for transferring and releasing the preforms and/or the blow-moulded containers after the blow-moulding phase.
Largely known in the art are also the problems connected to the start-up of a single-stage plant. In particular, when such plants are being started, the need arises technically for the plant to be brought to steady-state conditions, which means the need for the blow-moulding moulds, and in particular the injection moulds in the stage where the preforms are extruded/injection-moulded, to be brought to a pre-determined temperature, before preforms with the desired properties can be obtained.
As a result, after the plant has been started, a certain quantity of preforms are unavoidably produced for a certain period of time, or number of cycles, which, owing to the preforms not yet having the desired properties, cannot be used and must therefore be discarded.
To this purpose, such a type of plant is therefore started initially so that only the section thereof devoted to the production of preforms is actually operated, wherein the preforms, after having been removed from the moulds, are handled and transferred in the usual manner, and are eventually moved across the blow-moulding station. Since such preforms are not yet capable to be used for blow forming, owing to the above cited reasons, the blow-moulding station is not yet operating and, as a consequence, the preforms move, without being actually processed, between the two blow-forming mould halves which remain in their open position.
When they move out of the mould halves, the preforms, which are usually organized in groups that move in a synchronized manner, otherwise known as xe2x80x9cpreform trainsxe2x80x9d in the art, are transported, with generally per sxc3xa8 known means, towards an ejection station where they are separated from the plant and usually discharged into appropriate bins or containers. Anyway, they are eliminated from the production process.
After a certain period of initial operation, the plant then reaches steady-state conditions, so that it can from then on be operated in all of its sections.
As a consequence, the blow-moulding station is then running, so that the preforms are blow formed there and converted into finished containers which are again transported, in the same manner as illustrated above, to the ejection station that discharges them into appropriate baskets, bins or similar containers adapted to collect the finished product, from which they are then brought to the utilization plants, which are usually the filling plants.
Therefore, it clearly emerges that the need for two groups of products to be separated, i.e., the preforms or the blow-formed containers that are produced during the two subsequent phases of operation under start-up and steady-state conditions of the plant, practically involves the need for a phase to be provided of selective separation from the plant and, therefore, also of selective separation of the containers that are blow-moulded after the steady-state conditions of the plant have been reached.
It clearly ensues that such a need for a selective separation phase to be included and operating even after the plant has reached steady-state conditions, causes the orderly and substantially continuous flow of containers from the blow-moulding station to the utilization plants thereof to be practically interrupted. As a result, such a separation phase generates a considerable diseconomy since it practically prevents the production flow of blow-moulded containers from being automatically synchronized with the utilization flow of the same containers in the plants, such as filling plants, provided downstream.
As far as two-stage plants are concerned, i.e., practically the preform temperature conditioning station and the blow-moulding station, the situation is substantially similar to the one that has been just described with reference to single-stage plants, owing to a persisting need for a start-up phase to be provided in order to bring all of the various sections of the plant up to steady-state temperature.
Also in connection with two-stage plants, therefore, the need still arises for an initial run of preforms to be produced, which must then be xe2x80x9cdiscardedxe2x80x9d and separated selectively from the plant, so that the same drawbacks and diseconomies as the aforementioned ones are encountered also in these kind of plants.
Therefore, the need arises of providing an apparatus able to sequencially carry a plurality of containers and to release them in a transfer means apt to engage them and to move them from a specific working station to a different one. From EP 0 596 487 a transfer means of containers is known that is mainly using a moving chain operated in a closed loop. However, such a means appears to be rather complicated and burdensome both in the construction and during operation. Furthermore, it is missing of automatic means of expulsion, collecting and transfering of the containers as they reach a specific working station.
In consideration of what has been stated above, it is therefore a man purpose of the present invention to provide an apparatus and a method applying to the phases that follow the actual blow-moulding phase of a plant for the production of blow-moulded containers, so as to eliminate all of the above cited drawbacks and enable such the plant to feed in a substantially continuous and automatic manner the utilization plants arranged downstream, without any interposition of phases that are non-automatic or such as to anyway cause the continuity of flow of blow-moulded containers feeding such utilization plants to be interrupted. Furthermore, such an apparatus must be easily implemented through the use of readily available techniques and, therefore, be a reasonably low-cost one.
Such a main aim of the present invention, along with further features thereof, is reached in an apparatus that is made and operates as recited in the appended claims.